1. Technical Field
This invention relates to telephone conferencing arrangements and more particularly, to arrangements for identifying locations and directions of remote sound sources.
2. Description of the Prior Art
In current telephone conferencing arrangements, multiple parties participating at a telephone station receive only audio information from other parties participating at one or more remote telephone stations. No information is provided as to the remote location of a participant who is speaking or the identity of that participant. This limitation is present in existing analog and digital network telephone conferencing arrangements.
With digital networks, however, methods are now available that allow simultaneous transmission of both high quality telephony and data at a moderate speed. These methods are set forth in CCITT Recommendations G.722, G.725 and H.221 which allow for transmission of analog signals with a 7 kHz bandwidth along with optional data at rates at 6.4 or 14.4 kilobits per second over a digital channel. Such a digital channel currently supports only digitized 3 kHz audio signals (Recommendation CCITT G.711). The optional data provided over this digital channel is typically that which is used for communicating digital information between personal computers or facsimile machines.
A stereo signal may be used to convey information as to which participant in a telephone conference call is speaking. This generally requires employing a separate channel for both a left-direction signal and for a right-direction signal. The requirement of the two telephone channels, however, makes this both a cumbersome and expensive option.
An alternative to using two telephone channels for transmitting the stereo signal is to employ one of known signal processing schemes to reduce the digital bandwidth of the encoded signal. Typical of this type of signal processing is a perceptual entropy-based coder wherein a wide-bandwidth analog signal is digitized and encoded into a digital stream whose bandwidth is much less than that of the unprocessed digitized signal. This method, or a similar method, could be used to encode the stereo signals into a lower bit rate digital stream which could then be transmitted over a single digital channel of the digital network. The hardware and/or software to perform this type of encoding, however, is complex and expensive.
While the above methods employing a stereo signal can convey information as to which participant in a telephone conference call is speaking, they do not allow both high quality telephony and speaker location information to be economically conveyed over a single digital telephone channel.